Shallow junction implants are used in the formation of devices such as deep submicron metal oxide semiconductor ("MOS") transistors. In order to provide a shallow junction implant, a controlled surface is used to prevent contaminants from reaching the junction. Conventional processing methods in manufacturing provide a screening oxide prior to implantation. This screening oxide is on the order of fifty to one hundred Angstroms thick. The screening oxide is typically provided by exposing the silicon to oxygen gas at an elevated temperature, typically between eight hundred and one thousand degrees Centigrade. The screening oxide not only prevents contaminants from reaching the underlying silicon, but also reduces ion channeling.
Currently, semiconductor technology has been increasingly driven to lower device size. As the feature size shrinks, the gate length and, therefore, junctions shrink For example, gate lengths are shrinking to be on the order of 0.13 microns and below. Consequently, a method for providing shallow junction implants for smaller devices is needed.
The screening oxide may not be scaleable to smaller feature sizes. The thickness of the screening oxide requires higher implant energies which result in deeper implants. Consequently, screening oxides of conventional thicknesses are not used. In addition, the process for forming the screening oxide becomes difficult to control when lower oxide thicknesses are desired, often resulting in films of an uncontrolled and nonuniform thickness at thicknesses lower than the present screening oxides.
Most research in shallow junction implants for smaller feature sizes provides a controlled surface for implantation by stripping the screening oxide or native oxide from the surface of the silicon on which the junction is to be formed. This procedure is performed just prior to implantation. Thus, the shallow junction implant can be performed without interference from a native surface oxide. However, this procedure is difficult to implement in a large scale manufacturing process for two reasons. First, it requires cleaning a wafer prior to implantation, which is not conventionally done. Second, to limit native oxide growth prior to implantation, the implantation must occur within a predetermined time after the wafer is cleaned. Thus, a queue time, a maximum time specified between processes, is introduced. A manufacturing facility will, therefore, have to coordinate the cleaning and implantation steps to occur with the queue time. This introduces a strain on the manufacturing facility's resources and may result discarding or reworking of substantial quantities of devices when the queue time cannot be met. In addition, the beneficial control of contaminants provided by a screening oxide is lost.
Accordingly, what is needed is a system and method for controlling the surface of a semiconductor prior to a shallow junction implant that is suitable for a manufacturing process and capable of use with smaller feature sizes. The present invention addresses such a need.